This invention relates to refrigeration machines using the vaporization of a refrigeration fluid to produce cold. In conventional 1-stage installations, the refrigeration fluid in vapor phase is compressed, condensed with heat delivery to an external fluid, most often water or air, and then expanded and supplied to the vaporization step.
When attempting to obtain relatively low refrigeration temperatures by this process, for example, temperatures lower than -40.degree. C., it is found that the yield of the installation, which may be defined as the ratio of the refrigeration power obtained to the mechanical power consumed, sharply decreases when the desired refrigeration temperature itself decreases. This yield can be improved by operating with two stages in series, which permits attainment of a temperature of -100.degree. C.
To avoid a doubling of the equipment employed, it is also possible to operate according to the technique of the French Pat. No. 2,314,456. This technique is described herein with reference to the schematic diagram of FIG. 1.
The refrigeration fluid vaporizes in exchanger E2 with cooling of an external fluid. It is then recycled to compressor K1 either directly or through exchanger E1, (the latter arrangement is shown in FIG. 1). The compressed vapor phase VFC is admixed with a solvent phase S. The mixture of the vapor phase VFC with the solvent phase passes through the exchanger C1 where the vapor phase condenses in the presence of the solvent. The resultant liquid phase is cooled in exchanger E1. When using adapted solvent-solute pairs, phase separation occurs with formation of two liquid phases, including a phase of high solvent content and a phase of high refrigeration fluid content, which phases are collected in the decantation drum B1. The solvent phase is carried along by pump P1 and recycled through exchanger E1. The liquid phase of high refrigeration fluid content is expanded through the expansion valve V1 and supplied to exchanger E2.
When analyzing the way this process operates, it is found that the temperature T.sub.d of the mixture of the refrigeration fluid with the solvent withdrawn from exchanger E1 and collected in drum B1 is an essential parameter. The lower this temperature T.sub.d, the lower the concentration of refrigeration fluid in the solvent phase recycled from the drum B1. There results, when this temperature T.sub.d is decreased, the possibility to reduce the solvent recirculation rate and also the dissolution pressure.
When operating according to FIG. 1, the cooling of the mixture of solvent and solute discharged from condenser C1 is obtained by exchange with the solvent phase withdrawn from drum B1 and the vapor phase withdrawn from exchanger E2. In these conditions, there is no possibility to adjust the temperature T.sub.d ; on the other hand, because the calorific capacity of the refrigeration fluid in vapor phase is largely lower than the calorific capacity of the refrigeration fluid in liquid phase, this temperature T.sub.d cannot be decreased to a value close to the temperature attained in exchanger E2.